An internal combustion engine of this kind can be e.g. gasoline or diesel powered. Increasingly stringent legal requirements in respect of permissible pollutant emissions by motor vehicles fitted with internal combustion engines make it necessary to keep the pollutant emissions as low as possible during operation of the internal combustion engine. One of the ways in which this can be done is by reducing the emissions which occur during combustion of the air/fuel mixture in each cylinder of the internal combustion engine. Another is to use exhaust aftertreatment systems in internal combustion engines which convert the emissions produced during the combustion process of the air/fuel mixture in each cylinder into harmless substances. The common feature of all the approaches is that that precise determination of operating variables, particularly engine load, can provide a suitable means of minimizing the pollutant emissions.
Moreover, exacting requirements with regard to drivability also necessitate precise determination of operating variables such as, in particular, the load applied to the internal combustion engine.
In respect of lower raw emissions from combustion of the air/fuel mixture, the following approaches are employed: very high injection pressures, special injector designs, an ever increasing number of injections per operating cycle, improved mixture conditioning, higher exhaust gas recirculation rates and in this context also combustion methods such as homogeneous charge compression ignition. The common feature of all these approaches is that very precise knowledge of the cylinder pressure or rather the cylinder pressure variation during combustion is very important.
Depending on the spread of the flame front during combustion of the air/fuel mixture and the variable volume of the combustion chamber of the relevant cylinder as the piston travels, a pressure variation over time is produced which is heavily dependent on the filling of the combustion chamber. The cylinder pressure curve represents the sum of a large number of variables influencing engine operating behavior and is thus also very suitable as a command variable for controlling the internal combustion engine. Important for this purpose, however, is reliable and at the same time cost-effective cylinder pressure measurement.